(Continued from part I)
Case studies of failures help students understand the ethical and professional standards required of practicing engineers to prevent tragedies.
1. Cold weather affects concrete’s strength
Case IV: Willow Island – cooling tower collapsed, 1978.
One of the worst construction accidents in U.S history occurred on April 27, 1978. Fifty-one workers were killed at a nuclear power plant when a cooling tower under construction failed. A jump form was being used, with the form secured by bolts embedded in 1-day and 3-day-old concrete. The jump form progressively moved up to tower as it was built. During the evening before the failure, the temperature was in the mid 30s F. The National Bureau of Standards report found that the concrete had not attained sufficient strength to support the forms. The report concluded “the most probable cause of the collapse was the imposition of construction loads on the shell before the concrete had gained adequate strength to support these loads.
Case V: 2000 Commonwealth Ave., Boston, 1970
Four workers were killed and 20 were injured in a collapse that occurred on January 25, 1970 in Boston, U.S. An investigation into the collapse of the 17-story concrete high-rise under construction at 2000 Commonwealth Avenue disclosed a number of irregularities and deficiencies, including, among others: “insufficient concrete strength, insufficient length of reinforcing bars, lack of proper field inspection, various structural design deficiencies, improper formwork, premature removal of formwork, inadequate placement of reinforcing bars, lack of construction control”. Cool temperature that retarded strength gain were major factors in the disaster; the cores showed concrete strength as low as 700 psi (4.8 MPa).
Nuclear power plant: Nhà máy điện hạt nhân
Cool tower: Tháp làm mát.
Jump form: Ván khuôn trượt
Embed: Gắn vào
Bolt: bu long
Attain: đạt được
Support: chống đỡ, chịu (lực)
Load: Tải trọng
Shell: Khung hoặc vỏ chịu lực, trong bài có nghĩa là thành của tháp làm mát
Irregularity: Sự trái nguyên tắc
Deficiency: Sự yếu kém, khiếm khuyết
Reinforcing bar: Cốt thép chịu lực
Improper: Sai, không phù hợp
Inadequate: Không đủ, thiếu
Core: Mẫu khoan (bê tông)
Retard: Kéo dài
Field Inspection: Giám sát hiện trường
2. CRACKS INCONCRETE AFFECT SHEAR CAPACITY
If you do not allow for shrinkage and expansion volume changes, stress buildup can lead to damage or structural failure… (Continued soon in part III)
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